title: Anatomic characteristics of anal fistula on three-dimensional anorectal ultrasonography.
abstract: BACKGROUND
  Surgery for anal fistula is often associated with continence disorders due to the transection of sphincter muscles. Extensive knowledge of anal canal anatomy and anal fistula can help prevent this outcome.
  
  
  OBJECTIVE
  This study aimed to correlate the anatomical conformation of the anal canal, the fistula track, and the internal opening according to sex and hemicircumference (anterior vs posterior) by use of 3-dimensional ultrasonography.
  
  
  METHODS
  One hundred sixty-five patients with fistula were evaluated with 3-dimensional ultrasound and grouped according to sex, fistula type, internal opening, and track position. Fistulas were transsphincteric in 128 subjects and intersphincteric in 37 subjects. The study measured the external and internal anal sphincter, the puborectalis, the distance from the internal opening to the distal edge of the external and internal sphincter, the length of the internal and external sphincter compromised by the track, and the percentage of compromised muscle.
  
  
  RESULTS
  The anal canal muscles were longer in males. The distance from the internal opening to the internal sphincter was greater for the posterior hemicircumference. The point where the fistulous track crossed the anterior external sphincter was similar for the 2 sexes, but the percentage of compromised muscle was greater in females. The point where the fistulous track crossed the internal sphincter was similar for the 2 sexes, but the percentage of compromised internal sphincter was greater in males for the posterior hemicircumference. The study was limited by the absence of testing for interobserver and intraobserver agreement.
  
  
  CONCLUSIONS
  The anal canal muscles are longer in males and the pectinate line is asymmetrical. In females, the percentage of compromised external sphincter was greater in the anterior hemicircumference because of the shorter external sphincter, whereas in males the percentage of compromised internal sphincter was greater in the posterior hemicircumference.
authors.affiliation: Department of Surgery, School of Medicine of the Federal University of Ceará, Ceará, Brazil. smregadas@hospitalsaocarlos.com.br
authors.forename: Sthela M
authors.initials: SM
authors.lastname: Murad-Regadas
authors.forename: Francisco Sergio Pinheiro
authors.initials: FS
authors.lastname: Regadas
authors.forename: Lusmar Veras
authors.initials: LV
authors.lastname: Rodrigues
authors.forename: Graziela Olivia da S
authors.initials: GO
authors.lastname: Fernandes
authors.forename: Guilherme
authors.initials: G
authors.lastname: Buchen
authors.forename: Viviane T
authors.initials: VT
authors.lastname: Kenmoti
authors.forename: Gabriel Dos Santos Dias
authors.initials: Gdos S
authors.lastname: Soares
authors.forename: Erico de Carvalho
authors.initials: Ede C
authors.lastname: Holanda
mesh_terms: D000328:Adult; D001003:Anal Canal / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D019160:Endosonography / Q000379:methods*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D009130:Muscle, Smooth / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D012003:Rectal Fistula / Q000000981:diagnostic imaging*; D012189:Retrospective Studies; D012737:Sex Factors